Abstract: Most steel beam-column connections actually show semi-rigid deformation behavior that can contribute substantially to overall displacements of the structure and to the distribution of member forces. Steel frame structure with semi-rigid connections are becoming more and more popular due to their many advantages such as the better satisfaction with the flexible architectural design, low inclusive cost and environmental protect as well. So it is very necessary that studying the behavior of those steel frame under cyclic reversal loading. On the basics of connections experiments the experiment research on the lateral resistance system of steel frame structure has been completed. Two one-second scale, one-bay, two-story steel frames with semi-rigid connections under cyclic reversal loading. The seismic behavior of the steel frames with semi-rigid connections, including the failure pattern, occurrence order of plastic hinge, hysteretic property and energy dissipation, etc, was investigated in this paper. Some conclusions were obtained that by employing top-mounted and two web angles connections, the higher distortion occurred in the frames, and the internal force distributing of beams and columns was changed, and the ductility and the absorbs seismic energy capability of steel frames can be improved effectively.

Abstract: A two-span, three-story steel frame with two web and top-seat angle connections was constructed. Then a low-cycled reverse loading experiment with this frame was conducted to obtain elastic-plastic behavior of semi-rigid connections steel frame under cyclic loading. And nonlinear finite element analysis of steel frame with semi-rigid and rigid connection is performed in this paper. At last, comparisons between the analysis results and the testing results are carried out, the behavior and the effects of the two web and top-seat angles connections on steel frame are analyzed.

Abstract: Autoclaved lightweight concrete (ALC) block infills are used widely for steel residential building system in China; the authors of this paper brought forward a kind of macro finite element (FE) model of ALC block infills of steel frames on the basis of experimental study. Furthermore the hysteresis model of the strut element of infill was established. At last the validity of the strut element was verified by comparison theory analysis results with experiment ones. The analysis method and theory of this paper can be applied to other kind of infills after being revised properly.

Abstract: According to earthquake hazard, normal frame structures could hardly avoid failure of ‘Strong Beam and Weak Column’, weak layer and even progressive storey collapse under strong earthquakes, a main reason is the lack of second seismic fortification line in frame structure. Based on the design thought of multiple seismic fortification lines, reinforced concrete twin-frame structure is initiated in this paper. Major feature is increases of redundant constraints and load paths due to added outer limb-columns could take effect as the second seismic fortification line. Twin-frame structure could not only fulfill the demand of ‘three levels, two stages’ in seismic code, but also have been designed through the third stage of ‘resist progressive collapse’, using key member method to promote safety storage and deformability of outer limb-columns, using removal key member method to verify vertical ultimate load of frame beams in weak layer. Though twin-frame structure could not completely avoid plastic hinges in column ends, progressive storey collapse will not appear in this kind of structure. Twin-frame structure is a new structure system which could be applied in constituting new projects as well as strengthening and rebuilding existing projects, further research can be done on this structure system.

Abstract: In conventional analysis and design, the beam-column connections are divided into two categories: fully rigid joints and perfectly pinned joints. Actually, most beam-column connections exhibit flexibility. Idealized connections may diverge from the real reaction of structures. This article presents a hybrid finite-element model that consists of a beam element with two semi-rigid connections at the ends for studying the effect of the flexibility on the structures. Based on the theory of finite deformation, the first-order and the second-order stiffness matrix and the equilibrium equation of hybrid beam element were got. A nonlinear finite element analysis program was developed to analysis the steel frames with semi-rigid connections. At last, one-bay, two-story semi-rigid planar steel frame was analyzed using the program, and some conclusions about the effect of semi-rigid connections flexibility were obtained.